1. Technical Field
The present invention relates to a motor controller.
2. Related Art
In motors such as a blower motor employed to convey air in a vehicle air conditioner, overload protection control is performed to stop rotation of the blower motor in cases in which fan rotation is obstructed by a foreign object, such as a fallen leaf that has entered from outside the vehicle, increasing the load on the blower motor. Such overload protection prevents overheating due to overloading of circuits in the blower motor controller and in the coils of the stator of the blower motor.
FIG. 24 is a schematic view illustrating an example of a motor controller that determines motor overload based on a current value between an inverter circuit 40 and the negative electrode of a battery 80. In FIG. 24, a current detection section 94 is provided between the sources of respective inverter FETs 44D, 44E, and 44F and the battery 80. The current detection section 94 includes a shunt resistor 94A, and an amplifier 94B that detects a current value of the shunt resistor 94A and amplifies the detected current value. A signal output from the amplifier 94B is input into an overload determination section 98 and an overcurrent determination section 102 respectively.
The overcurrent determination section 102 compares the signal output from the amplifier 94B against an overcurrent determination value output from an overcurrent determination value output section 100, and the overload determination section 98 compares the signal output from the amplifier 94B against an overload determination value output from the overload determination value output section 96. Signals output from the overcurrent determination section 102 and the overload determination section 98 are input into an OR circuit 130.
The OR circuit 130 outputs a signal to forcibly stop the output of a voltage correction section 68 in a case in which the signal output from the amplifier 94B has been determined to be the overcurrent determination value or higher by the overcurrent determination section 102, or has been determined to be the overload determination value or higher by the overload determination section 98. The rotation of a motor 52 can accordingly be stopped when the circuit has been determined to be in an overloaded state or an overcurrent state, enabling circuit burnout to be prevented.
Vehicle air conditioner air intake systems are provided with filters to prevent the intrusion of foreign objects, however since such filters can create intake resistance, sometimes vehicle air conditioners are employed with the filters removed. Removing the filter from the air intake system increases the airflow of the air conditioner; however, since revolution control maintains the blower motor at the same rotation speed, the blower motor is liable to reach a high torque (high load).
In a blower motor, circuits, for example in the motor controller, are cooled by a portion of the air conveyed by the fan. However, when there is a large change to the airflow of the fan with the air intake system filter in a removed state, it is not possible to guide a portion of the airflow from the fan to cool the circuits, rendering the circuits liable to overheating.
When the load on the blower motor has increased, overload protection control is performed to stop rotation of the blower motor in order to prevent the motor controller from overheating. However, there is an issue that when the air intake system filter has been removed, making the blower motor liable to excessive rotation speed, such overload protection control is performed frequently, and as such, smooth operation of the vehicle air conditioner cannot be anticipated.
Patent Document 1 (Japanese Patent No. 3801015) discloses an overload protection device of a motor drive system that prevents overheating of a circuit by lowering the level of a motor rotation speed instruction signal in cases in which the temperature of a shunt resistor, disposed on a drive power supply path to a motor, has reached a specific temperature.